This book seeks to explore the potentialities of strengthening a new field of research within migration and diversity studies, that of immigrant incorporation in political parties. The point of departure of all the contributions to this volume is that there is what we call a ‘diversity gap’ between political parties as public representative organisations and diversity dynamics in democratic societies. Exploring the current strategies of political parties developing first conceptual frameworks, theoretical foundations and empirical hypothesis and approaches, this book examines case studies from four European countries: Germany, Ireland, Portugal and Spain. This book was originally published as a special issue of Ethnic and Racial Studies.